Magnetic disk apparatus and cipher key updating method

Abstract

According to one embodiment, a magnetic disk apparatus comprises a magnetic disk configured to store encrypted data, a magnetic head configured to read data from and to write data to the magnetic disk, and a recording and reproducing circuit connected to the magnetic head, wherein the recording and reproducing circuit configured to read data from an area of the magnetic disk, to decrypt read data, to re-encrypt decrypted data with changing a cipher key, and to rewrite re-encrypted data in the area of the magnetic disk.

1 . A magnetic disk apparatus comprising:
 a magnetic disk configured to store encrypted data;   a magnetic head configured to read encrypted data from the magnetic disk and to write encrypted data to the magnetic disk; and   a recording and reproducing module connected to the magnetic head,   wherein the recording and reproducing module is configured to read encrypted data from an area of the magnetic disk, to decrypt the read data, to re-encrypt decrypted data with a cipher key updated from previous encryption, and to rewrite re-encrypted data in the area of the magnetic disk.   
     
     
         2 . The apparatus of  claim 1 , wherein the recording/reproducing module comprises:
 a determination module configured to count a number of data writing for an area of the magnetic disk, and to determine whether the number of data writing for the area is larger than a predetermined number; and   an update module configured to read encrypted data from the area, to decrypt the read data, to re-encrypt the decrypted data with the updated cipher key, and to rewrite re-encrypted data in the area when the determination module determines that the number of data writing is larger than the predetermined number.   
     
     
         3 . The apparatus of  claim 2 , wherein the update module comprises a key storage module configured to store a predetermined number of cipher keys, and a table configured to store information indicative of cipher keys for areas, and to update information in the table after reading and decrypting encrypted data. 
     
     
         4 . The apparatus of  claim 3 , wherein the key storage module and the table are in a security area of the magnetic disk. 
     
     
         5 . The apparatus of  claim 2 , wherein the update module is configured to rewrite encrypted data in the area after writing re-encrypted data with the updated key in a backup area different from the area. 
     
     
         6 . The apparatus of  claim 2 , wherein the area comprises tracks, and a backup area comprises a predetermined number of tracks. 
     
     
         7 . The apparatus of  claim 2 , further comprising:
 a test module configured to perform a self test of the magnetic disk; and   a second update module configured to decrypt encrypted data read during the self test, to re-encrypt decrypted data with a cipher key updated from previous encryption, and to rewrite re-encrypted data.   
     
     
         8 . A recording and reproducing apparatus configured to read encrypted data from and write encrypted data into a magnetic disk, the apparatus comprising:
 a data refresh module configured to read data from an area of the magnetic disk, to decrypt the read data, to re-encrypt decrypted data with a cipher key updated from previous encryption, and to rewrite re-encrypted data in the area of the magnetic disk.   
     
     
         9 . The apparatus of  claim 8 , further comprising:
 a determination module configured to count a number of data writing for an area of the magnetic disk, and to determine whether the number of data writing is larger than a predetermined number; and   an update module configured to read encrypted data from an area, to decrypt the encrypted data, to re-encrypt the decrypted data with the updated cipher key, and to rewrite re-encrypted data in the given area when the determination module determines that the number of data writing is larger than the predetermined number.   
     
     
         10 . The apparatus of  claim 9 , wherein the update module comprises a key memory configured to store a predetermined number of cipher keys, and a table configured to store information indicative of cipher keys for areas, and to update information in the table after reading and decrypting encrypted data. 
     
     
         11 . The apparatus of  claim 9 , wherein the update module is configured to rewrite encrypted data in the area after writing re-encrypted data with the updated key in a backup area different from the given area. 
     
     
         12 . The apparatus of  claim 8 , further comprising:
 a test module which performs a self test of the magnetic disk; and   a second update module configured to decrypt encrypted data read during the self test, to re-encrypt decrypted data with a cipher key updated from previous encryption, and to rewrite re-encrypted data in a same area.   
     
     
         13 . A method of updating a cipher key of encrypted data stored on a magnetic disk, comprising:
 counting a number of data writing for an area of the magnetic disk to determine whether the number of data writing is larger than a predetermined number; and   reading encrypted data from an area of the magnetic disk, decrypting the read data, re-encrypting the decrypted data with the updated cipher key, and rewriting re-encrypted data in the area of the magnetic disk when it is determined that the number of data writing is larger than a predetermined number.   
     
     
         14 . The method of  claim 13 , wherein the re-encrypted data is rewritten in the area after the re-encrypted data is written in a backup area different from the area. 
     
     
         15 . The method of  claim 13 , further comprising:
 performing a self test of the magnetic disk; and   decrypting encrypted data read during the self test, re-encrypting decrypted data with a cipher key updated from previous encryption, and rewriting re-encrypted data.